Spin current generator for STT-MRAM or other spintronics applications

ABSTRACT

Spin current generators and systems and methods for employing spin current generators. A spin current generator may be configured to generate a spin current polarized in one direction, or a spin current selectively polarized in two directions. The spin current generator may by employed in spintronics applications, wherein a spin current is desired.

BACKGROUND

1. Field of Invention

The invention relates generally to current generators, and moreparticularly, to spin current generators for spintronics applications.

2. Description of Related Art

This section is intended to introduce the reader to various aspects ofthe art that may be related to various aspects of the present invention,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentinvention. Accordingly, it should be understood that these statementsare to be read in this light and not as admissions of prior art.

The development of microelectronics has led to large increases inintegration density and efficiency. However, the conventional electronicmethods of operation by applying voltage to control electron charge arefundamentally limited. Further improvements in nonvolatility, speed, andsize of electronic devices may require advancements in new technology.Spintronics, or spin electronics (also known as spin transportelectronics and magnetoelectronics), refers to the study of the spin ofan electron in solid state physics and the possible devices that mayadvantageously use electron spin properties instead of, or in additionto, the conventional use of electron charge.

The spin of an electron has two states and is characterized as beingeither “spin up” or “spin down.” Conventional spintronics devices haverelied on systems that provide bidirectional current to alter theelectron spins in the device. For example, one spintronics applicationinvolves data storage through a spintronics effect known as giantmagnetoresistance (GMR). The GMR structure includes alternatingferromagnetic and nonmagnetic metal layers, and the magnetizations andelectron spins in each of these magnetic layers provide resistancechanges through the layers. The resistance of the GMR may change fromlow (if the magnetizations are parallel) to high (if the magnetizationsare antiparallel), and the inducing and detecting of suchmagnetoresistance changes are the basis for writing and reading data.Another example of spintronics devices includes spin torque transfermagnetic random access memory (STT-MRAM). STT-MRAM also exploitselectron spin polarity by utilizing the electron spin to switch themagnetization of ferromagnetic layers to provide two programmable statesof low and high resistance.

This alteration of magnetization typically employs a bidirectionalprogramming current to change the magnetizations of the layers in amemory cell. However, bidirectional programming logic requires more cellspace. A transistor select device is required for each memory cell, andthis also increases the cell area. Furthermore, bidirectionalprogramming logic is generally more complicated and less efficient thanunidirectional programming logic.

BRIEF DESCRIPTION OF DRAWINGS

Certain embodiments are described in the following detailed descriptionand in reference to the drawings in which:

FIG. 1 depicts a block diagram of a processor-based system in accordancewith an embodiment of the present technique;

FIG. 2 depicts a device architecture and method by which a spin currentgenerator may enable a spintronics device in accordance with embodimentsof the present technique;

FIG. 3 depicts a spin current generator capable of generatingnon-polarized or adjustably polarized current in accordance withembodiments of the present invention; and

FIG. 4 depicts a spin current generator capable of generating adjustablypolarized current in accordance with embodiments of the presentinvention.

DETAILED DESCRIPTION

Spintronics devices write and store information by manipulating electronspin in a particular orientation. As previously discussed, informationmay be stored by programming magnetic layers in a memory cell into lowresistance and high resistance states. Switching between the tworesistance states typically employs a bidirectional programming current,where a current passed in one direction may orient the magnetization ofmemory cell layers to a low resistance state, and a current passed in anopposite direction may orient the magnetization of memory cell layers toa high resistance state. Since bidirectional programming logic requiresmore complicated circuitry and more chip space, a method of generatingelectron currents with desired spin polarizations may reduce thecomplexity and size of memory cell area or other devices requiringcurrents of different polarities by facilitating unidirectionalprogramming. The following discussion describes the systems and devices,and the operation of such systems and devices in accordance with theembodiments of the present technique.

FIG. 1 depicts a processor-based system, generally designated byreference numeral 10. As is explained below, the system 10 may includevarious electronic devices manufactured in accordance with embodimentsof the present technique. The system 10 may be any of a variety of typessuch as a computer, pager, cellular phone, personal organizer, controlcircuit, etc. In a typical processor-based system, one or moreprocessors 12, such as a microprocessor, control the processing ofsystem functions and requests in the system 10. As is explained below,the processor 12 and other subcomponents of the system 10 may includeresistive memory devices manufactured in accordance with embodiments ofthe present technique.

The system 10 typically includes a power supply 14. For instance, if thesystem 10 is a portable system, the power supply 14 may advantageouslyinclude a fuel cell, a power scavenging device, permanent batteries,replaceable batteries, and/or rechargeable batteries. The power supply14 may also include an AC adapter, so the system 10 may be plugged intoa wall outlet, for instance. The power supply 14 may also include a DCadapter such that the system 10 may be plugged into a vehicle cigarettelighter, for instance.

Various other devices may be coupled to the processor 12 depending onthe functions that the system 10 performs. For instance, a userinterface 16 may be coupled to the processor 12. The user interface 16may include buttons, switches, a keyboard, a light pen, a mouse, adigitizer and stylus, and/or a voice recognition system, for instance. Adisplay 18 may also be coupled to the processor 12. The display 18 mayinclude an LCD, an SED display, a CRT display, a DLP display, a plasmadisplay, an OLED display, LEDs, and/or an audio display, for example.Furthermore, an RF sub-system/baseband processor 20 may also be coupledto the processor 12. The RF sub-system/baseband processor 20 may includean antenna that is coupled to an RF receiver and to an RF transmitter(not shown). One or more communication ports 22 may also be coupled tothe processor 12. The communication port 22 may be adapted to be coupledto one or more peripheral devices 24 such as a modem, a printer, acomputer, or to a network, such as a local area network, remote areanetwork, intranet, or the Internet, for instance.

The processor 12 generally controls the system 10 by implementingsoftware programs stored in the memory. The software programs mayinclude an operating system, database software, drafting software, wordprocessing software, and/or video, photo, or sound editing software, forexample. The memory is operably coupled to the processor 12 to store andfacilitate execution of various programs. For instance, the processor 12may be coupled to the system memory 26, which may include spin torquetransfer magnetic random access memory (STT-MRAM), magnetic randomaccess memory (MRAM), dynamic random access memory (DRAM), and/or staticrandom access memory (SRAM). The system memory 26 may include volatilememory, non-volatile memory, or a combination thereof. The system memory26 is typically large so that it can store dynamically loadedapplications and data. In some embodiments, the system memory 26 mayinclude STT-MRAM devices, such as those discussed further below.

The processor 12 may also be coupled to non-volatile memory 28, which isnot to suggest that system memory 26 is necessarily volatile. Thenon-volatile memory 28 may include STT-MRAM, MRAM, read-only memory(ROM), such as an EPROM, resistive read-only memory (RROM), and/or flashmemory to be used in conjunction with the system memory 26. The size ofthe ROM is typically selected to be just large enough to store anynecessary operating system, application programs, and fixed data.Additionally, the non-volatile memory 28 may include a high capacitymemory such as a tape or disk drive memory, such as a hybrid-driveincluding resistive memory or other types of non-volatile solid-statememory, for instance. As is explained in greater detail below, thenon-volatile memory 28 may include STT-MRAM devices manufactured inaccordance with embodiments of the present technique.

Both the system memory 26 and the non-volatile memory 28 may includememory cells programmable by manipulation of electron spin or otherspintronics components. For example, the memory cells may include MRAMcells, STT-MRAM cells, or memory cells that utilize the giantmagnetoresistive (GMR) effect. The system memory 26 and the non-volatilememory 28 may further include a spin current generator to generatesingle-spin polarity current (i.e., a current that can be generated witha spin polarity in only one direction), bi-spin polarity current (i.e.,a current that can be generated with a spin polarity in eitherdirection), non-polarized current or arbitrary spin-polarized current toprogram the memory cells, as will be further described below.

FIG. 2 depicts an example of a portion of a spintronics device and amethod by which a spin current generator 100 may be used to program thedevice in accordance with embodiments of the present technique. Theportion of the spintronics device illustrated here includes an array 102of memory cell components 104 with magnetic layers 106 and 108. As willbe appreciated, each memory cell component 104 may form the memoryportion of a single memory cell in the array 102. The memory cellcomponents 104 may include magnetic tunnel junctions (MTJs), stacks offerromagnetic and nonmagnetic layers, or any other structure in whichmagnetization may be manipulated to alter the structure'smagnetoresistance state. Furthermore, the memory cell components 104 maybe components of magnetic random access memory (MRAM) cells, spin torquetransfer magnetic random access memory (STT-MRAM) cells, or any otherdevice exploiting the manipulation of electron spin to program the cell.

In this example, the memory cell component 104 includes a pinned layer106 and a free layer 108. A memory cell may be “written” or “programmed”by switching the magnetization of the free layer 108 in the memory cellcomponent 104, and the cell may be read by determining the resistanceacross the free layer 108 and the pinned layer 106. The layers 108 and106 may comprise ferromagnetic materials, such as Co, Fe, Ni or itsalloys, NiFe, CoFe, CoNiFe, or doped alloys CoX, CoFeX, CoNiFeX (X=B,Cu, Re, Ru, Rh, Hf, Pd, Pt, C), or other half-metallic ferromagneticmaterial such as Fe3O4, CrO2, NiMnSb and PtMnSb, and BiFeO, forinstance. The pinned layer 106 is so named because it has amagnetization with a fixed or pinned preferred orientation, and this isrepresented by the unidirectional arrow illustrated in the pinned layer106. An additional layer of antiferromagnetic material may be depositedbelow the pinned ferromagnetic layer to achieve the pinning throughexchange coupling. The bidirectional arrow illustrated in the free layer108 represents that the free layer 108 may be magnetized either in adirection parallel to the pinned layer 106, which gives a lowresistance, or in a direction antiparallel to the pinned layer 106,which gives a high resistance. The memory cell component 104 may alsoinclude a nonmagnetic layer between the free layer 108 and the pinnedlayer 106 to serve as an insulator between the two layers 108 and 106,thereby forming a MTJ structure in this example. The nonmagnetic layermay include materials such as AlxOy, MgO, AlN, SiN, CaOx, NiOx, HfO2,Ta2O5, ZrO2, NiMnOx, MgF2, SiC, SiO2, SiOxNy, for example.

The spin current generator 100 is connected to each memory cell in thearray 102 through source lines 110. In the presently illustratedembodiment, each of the memory cell components 104 is coupled in seriesto form a string, such that each of the memory cell components 104 iscoupled to a common source line 110. When a memory cell is selected tobe programmed, the spin current generator 100 sends a spin polarizedcurrent through the source line 110 to the selected memory cell andmemory cell component 104. If the memory cell is to be programmed to alow resistance state (“write 1 operation”) 114, the spin currentgenerator 100 will generate a current polarized in one direction (e.g.,to the left) 116, and the left-polarized current will switch themagnetization of the free layer 108 to the left. Because themagnetization of the pinned layer 106 is also directed to the left, themagnetizations of the free layer 108 and the pinned layer 106 areparallel, and the memory cell is programmed to a low resistance state.Likewise, if the memory cell is to be programmed to a high resistancestate (“write 0 operation”) 118, the spin current generator 100 willgenerate a current polarized in an opposite direction (to the right)120, and the right-polarized current will switch the magnetization ofthe free layer 108 to the right. Because the magnetization of the pinnedlayer 106 is directed to the left, the magnetizations of the free layer108 and the pinned layer 106 are antiparallel, and the memory cell isprogrammed to a high resistance state.

The method depicted in accordance with embodiments of the presenttechnique thus enables the memory cells or other spintronics devices tobe programmed by a unidirectional current, allowing for simplerunidirectional programming logic. As previously discussed, conventionalspintronics devices, including STT-MRAM devices, typically usebidirectional programming logic, meaning the write current is driven inopposite directions through a device cell stack to switch the cellbetween different programmable states. For example, in a STT-MRAM cell,a write current may be driven from a transistor source to a transistordrain, and then through a MTJ to program the memory cell to a highresistant state. To program a memory cell to a low resistance state, awrite current may be driven from a MTJ to a transistor drain to atransistor source. Unidirectional programming logic may be simpler andmore efficient than bidirectional programming logic. Also, the array 102may be fabricated without a separate transistor for each cell, whichfurther decreases cell size and cost. By utilizing a spin currentgenerator 100 which may generate a spin current polarized in eitherdirection (a bi-spin polarity current), the memory cell component 104may be programmed with a unidirectional current, as described furtherbelow. Further, in certain embodiments, a single-spin polarity current,or a non-polarized spin current may be utilized to program a memory cellcomponent 104, by adding certain features or layers to the memory cellcomponent 104, such that the memory cell component 104 is able toexploit the properties of the current to facilitate the changing of themagnetization of a free ferromagnetic layer, therein. For example, inFIG. 2, if a non-polarized current is passed through the memory cellcomponent 104, the the pinned layer 106 may reflect the current towardsthe free layer 108 and switch the magnetization direction of the freelayer 108 to the opposite direction of the pinned layer 106.

One embodiment of the present invention, a spin current generatorconfigured to generate a unidirectional current to adjust polarizationdirection in a spintronics device, is illustrated in FIG. 3, where aspin current generator 200 can generate a non-polarized current 212 or asingle-spin polarized current 214. The bidirectional arrows depictingthe non-polarized current 212 represent that the current is not yetpolarized in any direction. Conversely, the unidirectional arrowdepicting the polarized current 214 represent that the current ispolarized in one direction (single-spin polarized). The spin currentgenerator 200 includes a spin-polarizing layer 202, which may compriseferromagnetic materials, such as Co, Fe, Ni or its alloys, NiFe, CoFe,CoNiFe, or doped alloys CoX, CoFeX, CoNiFeX (X=B, Cu, Re, Ru, Rh, Hf.Pd, Pt, C), or other half-metallic ferromagnetic material such as Fe3O4,CrO2, NiMnSb and PtMnSb, and BiFeO, for instance. The spin currentgenerator 200 may also include a nonmagnetic layer 204 which may benonconductive and include some combination of AlxOy, MgO, AlN, SiN,CaOx, NiOx, HfO2, Ta2O5, ZrO2, NiMnOx, MgF2, SiC, SiO2, or SiOxNy, forexample, or conductive and include some combination of Cu, Au, Ta, Ag,CuPt, CuMn or other nonmagnetic transition metal, for example. Thespin-polarizing layer 202 and the nonmagnetic layer 204 may be isolatedfrom a material 206 by an insulative material 208. In some embodiments,the material 206 may generate heat (“heater material”), and in otherembodiments, the material 206 may comprise piezoelectric materials(“piezoelectric material”).

In some embodiments, the material 206 may incorporate some combinationof heat generating and piezoelectric materials, or the material 206 maycomprise more than one heat generating and/or piezoelectric material. Asused in the present specification, the term “layer” refers to materialsformed in parallel, with one material disposed over another (e.g.,layers 204, 202, and 210 of FIG. 3). In contrast other materials, notreferred to as layers, may be formed perpendicular to a stack ofparallel materials (e.g., layers 206 and 208 are perpendicular to layers204, 202, and 210 of FIG. 3), as spacers other structures formedadjacent to the layers. As also used herein, it should be understoodthat when a layer is said to be “formed on” or “disposed on” anotherlayer, the layers are understood to be parallel to one another, butthere may be intervening layers formed or disposed between those layers.In contrast, “disposed directly on” or “formed directly on” refers tolayers in direct contact with one another. Similarly, if materials aresaid to be “adjacent” to other materials, the materials are in the samecross-sectional plane (e.g., the layer 206 is adjacent to the layers202, 204 and 210). Further, if a material is said to be adjacent toanother material or layer, there may be intervening materialstherebetween, while “directly adjacent,” connotes no interveningmaterials therebetween.

Since heat decreases magnetization and spin-polarization efficiency inmagnetic materials, a heater material 206 may apply heat to decrease oreliminate the magnetization or spin polarization of the spin-polarizinglayer 202, and the spin current generator 200 may output a non-polarizedor less spin polarized current 212. Specifically, when voltage isapplied to the spin current generator 200 through the transistor 216,the heater material 206 may heat up the spin-polarizing layer close toor above its curie temperature, which may be in a range of approximately160° C. to 300° C. The spin-polarizing layer 202 would thensubstantially lose its magnetization, and current would be non-polarizedor not highly polarized after it passes through the demagnetizedspin-polarizing layer 202. The spin-polarizing layer 202 may retain itsmagnetization through an exchange interaction with the antiferromagneticlayer 210 when the spin-polarizing layer 202 is cooled to approximatelyroom temperature. Thus, the spin current generator 200 may produce aunidirectional non-polarized current to program a spintronics device.One example of how a unidirectional non-polarized current may program aspintronics device is to pass non-polarized current that becomes spinpolarized by magnetic layers of fixed magnetization in a spintronicsdevice. Further, magnetic layers may be switched by reflected currentspolarized by other layers in a spintronics device.

Alternatively, the spin current generator 200 may produce polarizedcurrent 214 of various polarization degrees through a transient stresseffect induced by the piezoelectric stress material 206. Thepiezoelectric stress material 206 may apply varying stress to adjust thespin polarization of the spin-polarizing layer 202. When voltage isapplied to the piezoelectric stress material 206 through the transistor216, the piezoelectric stress material 206 may induce a stress thatmodulates the spin-polarization efficiency of the spin-polarizing layer202 such that the current output of the spin current generator 200 maybe polarized to a desired degree.

Specifically, the spin polarization degree of the output current isdetermined by the spin-polarization efficiency of the spin-polarizinglayer 202, which may be adjusted by either heat or stress to thespin-polarizing layer 202. If the spin current generator 200 sends apolarized current 214 to a spintronics device, voltage may be applied tothe spin current generator 200, and the piezoelectric material 206 maygenerate a transient stress in the spin-polarizing layer 202. Thetransient stress influences the spin-polarization efficiency of thespin-polarizing layer 202, which affects the degree of polarization ofthe output current. Thus, embodiments in accordance with the presenttechnique may produce unidirectional single-spin polarized current toswitch the magnetization of a spintronics device. The direction of thespin current that may be output by the spin current generator 200 isdependent on the arrangement of the transistor 216, as will beappreciated.

The heater material 206 may comprise refractory metals including, forexample, nitride, carbide, and Boride, TiN, ZrN, HfN, VN, NbN, TaN, TiC,ZrC, HfC, VC, NbC, TaC, TiB2, ZrB2, HfB2, VB2, NbB2, TaB2, Cr3C2, Mo2C,WC, CrB2, Mo2B5, W2B5, or compounds such as TiAlN, TiSiN, TiW, TaSiN,TiCN, SiC, B4C, WSix, MoSi2, or elemental materials such as dopedsilicon, carbon, Pt, Niobium, Tungsten, molybdenum, or metal alloys suchas NiCr, for example. In some embodiments, the piezoelectric material206 may be composed of a conductive piezoelectric material, such as(TaSe4)2I, multi-layered AlxGa1-xAs/GaAs, BaTiO3/VGCF/CPE composites, orother piezoelectric/conductive material composites. In otherembodiments, the piezoelectric material 206 may be an insulativematerial, such as berlinite (AlPO₄), quartz, gallium orthophosphate(GaPO₄), langasite (La₃Ga₅SiO₁₄), ceramics with perovskite ortungsten-bronze structures such as barium titanate (BaTiO₃), SrTiO3,bismuth ferrite (BiFeO₃), lead zirconate titanate (Pb[Zr_(x)Ti_(1-x)]O₃0<x<1), Pb₂KNb₅O₁₅, lead titanate (PbTiO₃), lithium tantalate (LiTaO₃),sodium tungstate (Na_(x)WO₃), potassium niobate (KNbO₃), lithium niobate(LiNbO₃), Ba₂NaNb₅O₅, and other materials such as ZnO, AlN,polyvinylidene fluoride (PVDF), lanthanum gallium silicate, potassiumsodium tartrate, sodium potassium niobate (KNN). The nonmagnetic layer204 may insulate the magnetic layers of the spin current generator 200from other magnetic layers and may be either conductive ornonconductive. The conductive nonmagnetic layer 204 may comprise Cu, Au,Ta, Ag, CuPt, CuMn, or other nonmagnetic transition metals, or anycombination of the above nonmagnetic conductive materials. Thenonconductive nonmagnetic layer 204 may comprise Al_(x)O_(y), MgO, AlN,SiN, CaO_(x), NiO_(x), HfO₂, Ta₂O₅, ZrO₂, NiMnO_(x), MgF₂, SiC, SiO₂,SiO_(x)N_(y), or any combination of the above nonmagnetic nonconductivematerials.

Another embodiment of the present invention is illustrated in FIG. 4,where a spin current generator 300 can generate arbitrary spin currentor spin current polarized in either direction (bi-spin polarity). Asused in the present specification, arbitrary spin current refers to spincurrent polarized in either direction with any desired polarizationdegree. The spin current generator 300 uses two structures 302 and 304of opposite magnetization. Each structure has a respective spinpolarizing layer 306 and a nonmagnetic layer 308. The spin-polarizinglayer 306 in the structures 302 and 304 have opposite magnetizations,and this enables the spin current generator 300 to generate currentspin-polarized in an arbitrary degree for a spintronics device, or in aspecified direction based on the selection of the appropriate transistor314 or 316. The spin current generator 300 may be employed inapplications and systems benefiting from a spin current generatorcapable of producing a bi-spin polarity current (i.e., a current with aspin-polarity in either direction), such as the memory cells of FIG. 1.

For example, if a memory cell (as in FIG. 2) is selected to beprogrammed to a low resistance state, a current would pass through thestructure 304 of the spin current generator 300, via the transistor 316,where the spin-polarizing layer 306 polarizes the spin of the electronsto the left. The spin current generator 300 then outputs a programmingcurrent spin polarized to the left 310, and the left-polarized current310 switches the magnetization of free layer 108 (of FIG. 2) to theleft, parallel to the pinned layer 106, writing the cell in a lowresistance state. If a memory cell is selected to be programmed to ahigh resistance state, a current would pass through the structure 302 ofthe spin current generator 300, via the transistor 314, where thespin-polarizing layer 306 polarizes the spin of the electrons to theright. The programming current is spin polarized to the right 312, andthe right-polarized current 312 switches the magnetization of free layer108 to the right, antiparallel to the pinned layer 106, writing the cellin a high resistance state.

The spin-polarizing layer 306 may comprise ferromagnetic materials, suchas Co, Fe, Ni or its alloys, NiFe, CoFe, CoNiFe, or doped alloys CoX,CoFeX, CoNiFeX (X=B, Cu, Re, Ru, Rh, Hf, Pd, Pt, C), or otherhalf-metallic ferromagnetic material such as Fe3O4, CrO2, NiMnSb andPtMnSb, and BiFeO, for instance. The nonmagnetic layer 308 may insulatethe magnetic layers of the spin current generator 300 from othermagnetic layers and may be either conductive or nonconductive. Theconductive nonmagnetic layer 308 may comprise Cu, Au, Ta, Ag, CuPt,CuMn, or other nonmagnetic transition metals, or any combination of theabove nonmagnetic conductive materials. The nonconductive nonmagneticlayer 308 may comprise Al_(x)O_(y), MgO, AlN, SiN, CaO_(x), NiO_(x),HfO₂, Ta₂O₅, ZrO₂, NiMnO_(x), MgF₂, SiC, SiO₂, SiO_(x)N_(y), or anycombination of the above nonmagnetic nonconductive materials.

This embodiment and other embodiments in accordance with the presenttechnique may be used in spintronics applications, or in conjunctionwith or incorporated in any device using electron spin properties. As anexample, STT-MRAM cells are programmed into low or high resistancestates by switching the magnetization of a free ferromagnetic layer inthe memory cell. As previously discussed, the memory cell is programmedto a low resistance state when a programming current switches themagnetization of the free layer to be parallel with the magnetization ofa pinned layer in the STT-MRAM cell. The memory cell is programmed to ahigh resistance state when a programming current switches themagnetization of the free layer to be antiparallel with themagnetization of the pinned layer in the STT-MRAM cell. The typicalSTT-MRAM cell is structured with bidirectional programming logic, as thefree layer requires programming current polarized in both directions,depending on the resistance state it will be switched to. In theembodiments of the present technique, a spin current generator capableof generating current polarized in either direction, or not polarized atall, may allow for simpler unidirectional programming logic in theSTT-MRAM cell or other spintronics components.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. A spin current generator comprising: at least one structurecomprising a ferromagnetic layer and a nonmagnetic layer; and at leastone gate configured to selectively apply a voltage to the at least onestructure, wherein the spin current generator is configured to output acurrent.
 2. The spin current generator, as set forth in claim 1, whereinthe nonmagnetic layer is formed directly on the ferromagnetic layer, andwherein the at least one structure further comprises anantiferromagnetic layer, wherein the ferromagnetic layer is formeddirectly on the antiferromagnetic layer.
 3. The spin current generator,as set forth in claim 1, wherein the at least one structure comprises aninsulative material formed adjacent to the ferromagnetic layer and thenonmagnetic layer.
 4. The spin current generator, as set forth in claim1, wherein the at least one structure comprises a heater material formedadjacent to the ferromagnetic layer and the nonmagnetic layer.
 5. Thespin current generator, as set forth in claim 1, wherein the at leastone structure comprises a piezoelectric material formed adjacent to theferromagnetic layer and the nonmagnetic layer.
 6. The spin currentgenerator, as set forth in claim 1, wherein the at least one gatecomprises a transistor.
 7. The spin current generator, as set forth inclaim 1, wherein the spin current generator configured to generate acurrent having a spin polarity and further configured to generate anunpolarized current.
 8. The spin current generator, as set forth inclaim 1, wherein the at least one structure comprises: a first structurecomprising a first ferromagnetic layer and a first nonmagnetic layerformed directly on the first ferromagnetic layer; and a second structurecomprising a second ferromagnetic layer and a second nonmagnetic layerformed directly on the second ferromagnetic layer, wherein the firstferromagnetic layer and the second ferromagnetic layer are oppositelymagnetized.
 9. The spin current generator, as set forth in claim 8,wherein the at least one gate comprises a first transistor coupled tothe first structure and a second transistor coupled to the secondstructure.
 10. The spin current generator, as set forth in claim 8,wherein the spin current generator is configured to generate a spincurrent having a polarity parallel to a magnetization of the firstferromagnetic layer, and further configured to generate a spin currenthaving a polarity parallel to a magnetization of the secondferromagnetic layer.
 11. The spin current generator, as set forth inclaim 1, wherein the spin current generator is configured to generate aspin current having a first polarity, and further configured to generatea spin current having a second polarity.
 12. A system comprising: aprogrammable structure; and a spin current generator configured togenerate a spin current through the programmable structure.
 13. Thesystem, as set forth in claim 12, wherein the programmable structurecomprises a memory cell.
 14. The system, as set forth in claim 13,wherein the memory cell comprise a spin torque transfer magnetic randomaccess memory cell having a free layer and a pinned layer.
 15. Thesystem, as set forth in claim 14, wherein the spin current generator isconfigured to polarize the free layer to a first polarity, and furtherconfigured to polarize the free layer to a second polarity, opposite thefirst polarity.
 16. The system, as set forth in claim 12, wherein thespin current generator is configured to generate a spin current having afirst polarity, and further configured to generate a spin current havinga second polarity, opposite the first polarity.
 17. The system, as setforth in claim 12, wherein the spin current generator comprises: a firststructure configured to generate a spin current having a first polarity;and a second structure, parallel to the first structure, and configuredto generate a spin current having a second polarity, opposite the firstpolarity.
 18. The system, as set forth in claim 17, comprising one ormore gates configured to selectively transmit current through either thefirst structure or the second structure.
 19. The system, as set forth inclaim 17, wherein: the first structure comprises a first ferromagneticlayer and a first nonmagnetic layer formed directly on the firstferromagnetic layer; and the second structure comprises a secondferromagnetic layer and a second nonmagnetic layer formed directly onthe second ferromagnetic layer, wherein the first ferromagnetic layerand the second ferromagnetic layer are oppositely magnetized.
 20. Thesystem, as set forth in claim 12, wherein the spin current generatorcomprises a piezoelectric material.
 21. The system, as set forth inclaim 12, wherein the spin current generator comprises a heatermaterial.
 22. The system, as set forth in claim 21, wherein the spincurrent generator comprises a ferromagnetic layer, and wherein theheater material is configured to heat the ferromagnetic layer to reduceits spin-polarization efficiency.
 23. The system, as set forth in claim12, wherein the programmable structure comprises a plurality of memorycells coupled in series to one another, and wherein the spin currentgenerator is configured to generate a spin current through each of theplurality of memory cells.
 24. The system, as set forth in claim 23,wherein the spin current generator is configured to generate a spincurrent through each of the plurality of memory cells, simultaneously.25. A method of operating a device comprising: transmitting, from a spincurrent generator, a first current having a first polarity through astructure of the device in a first direction; and transmitting, from thespin current generator, a second current having a second polaritythrough the structure in the first direction, wherein the first polarityis opposite the second polarity.
 26. The method, as set forth in claim25, wherein transmitting the first current sets the structure into afirst state, and wherein transmitting the second current sets thestructure into a second state.
 27. The method, as set forth in claim 25,wherein transmitting through the structure comprises transmittingthrough a memory device.
 28. The method, as set forth in claim 27,wherein transmitting the first current programs the memory device into afirst state, and wherein transmitting the second current programs thememory device into a second state.
 29. The method, as set forth claim28, wherein transmitting the first current programs the memory deviceinto a low resistance state, and wherein transmitting the second currentprograms the memory device into a high resistance state.
 30. A method ofoperating a device comprising: transmitting, from a spin currentgenerator, a first current having a polarity through a structure of thedevice in a first direction; and transmitting, from the spin currentgenerator, a second current having a non polarity through the structurein the first direction.
 31. The method, as set forth in claim 30,wherein transmitting the first current sets the structure into a firststate, and wherein transmitting the second current sets the structureinto a second state.